Full Life-cycle Toxicity Test Research Articles

Bisphenol P activates hormonal genes and introduces developmental outcomes in Chironomus tentans

The endocrine disrupting properties of bisphenol A (BPA) discharged to the environment have been newly identified by the European Chemicals Agency, increasing the need to assess the environmental endocrine disrupting potentials of its alternatives with which it shares close structural features. However, few investigations of the environmental endocrine disrupting functions of BPA analogs have been conducted to date. In this study, the endocrine disrupting effects of a BPA analog of bisphenol P (BPP) were investigated in the nonbiting midge (Chironomus tentans), a model organism in ecotoxicology. An initial ex vivo test using salivary gland cells explanted from the larvae and a subsequent in vivo test using embryos and larvae revealed the upregulatory effects of BPP on ecdysone receptor genes encoding the ecdysone receptor (EcR) and the early responsive gene E74, with a similar temporal pattern of gene activation. Partial life cycle and full life cycle toxicity tests demonstrated BPP altered embryo hatching, larval emergence, and adult sex ratio at concentrations close to the effective concentrations for hormonal genetic endpoints in embryos and larvae after 48 h of exposure. Although embryos appeared to be more sensitive to BPP than the fourth instar larvae, the impact on neither life stage seemed enough to estimate the developmental impairment of the insects. These results demonstrate the ecdysone pathway is a target of BPP, and that long-term exposure could cause apical effects on the development of C. tentans. The endocrine disrupting effects towards aquatic organisms, as well as the high persistence and bioconcentration potential, indicate an urgent need to assess the environmental risks associated with BPP.

Comparative chronic toxicity of imidacloprid, clothianidin, and thiamethoxam to Chironomus dilutus and estimation of toxic equivalency factors.

Nontarget aquatic insects are susceptible to chronic neonicotinoid insecticide exposure during the early stages of development from repeated runoff events and prolonged persistence of these chemicals. Investigations on the chronic toxicity of neonicotinoids to aquatic invertebrates have been limited to a few species and under different laboratory conditions that often preclude direct comparisons of the relative toxicity of different compounds. In the present study, full life-cycle toxicity tests using Chironomus dilutus were performed to compare the toxicity of 3 commonly used neonicotinoids: imidacloprid, clothianidin, and thiamethoxam. Test conditions followed a static-renewal exposure protocol in which lethal and sublethal endpoints were assessed on days 14 and 40. Reduced emergence success, advanced emergence timing, and male-biased sex ratios were sensitive responses to low-level neonicotinoid exposure. The 14-d median lethal concentrations for imidacloprid, clothianidin, and thiamethoxam were 1.52 μg/L, 2.41 μg/L, and 23.60 μg/L, respectively. The 40-d median effect concentrations (emergence) for imidacloprid, clothianidin, and thiamethoxam were 0.39 μg/L, 0.28 μg/L, and 4.13 μg/L, respectively. Toxic equivalence relative to imidacloprid was estimated through a 3-point response average of equivalencies calculated at 20%, 50%, and 90% lethal and effect concentrations. Relative to imidacloprid (toxic equivalency factor [TEF] = 1.0), chronic (lethality) 14-d TEFs for clothianidin and thiamethoxam were 1.05 and 0.14, respectively, and chronic (emergence inhibition) 40-d TEFs were 1.62 and 0.11, respectively. These population-relevant endpoints and TEFs suggest that imidacloprid and clothianidin exert comparable chronic toxicity to C. dilutus, whereas thiamethoxam induced comparable effects only at concentrations an order of magnitude higher. However, the authors caution that under field conditions, thiamethoxam readily degrades to clothianidin, thereby likely enhancing toxicity. Environ Toxicol Chem 2017;36:372-382. © 2016 SETAC.

Effects of carbamazepine and two of its metabolites on the non-biting midge Chironomus riparius in a sediment full life cycle toxicity test

The antiepileptic drug carbamazepine (CBZ) and its main metabolites carbamazepine-10,11-epoxide (EP-CBZ) and 10,11-dihydro-10,11-dihydroxy-carbamazepine (DiOH-CBZ) were chosen as test substances to assess chronic toxicity on the non-biting midge Chironomus riparius. All the three substances were tested in a 40-day sediment full life cycle test (according to OECD 233) in which mortality, emergence, fertility, and clutch size were evaluated. In addition, these parameters were considered to calculate the population growth rate which represents an integrated measure to assess population relevant effects. With an LC50 of 0.20 mg/kg (time-weighted mean), the metabolite EP-CBZ was significantly more toxic than the parent substance CBZ (LC50: 1.1 mg/kg). Especially mortality, emergence, and fertility showed to be sensitive parameters under the exposure to CBZ and EP-CBZ. By using classical molecular dynamics (MD) simulations, the binding of CBZ to the ecdysone receptor was investigated as one possible mode of action (MoA) but appeared to be unlikely. The second metabolite DiOH-CBZ did not cause any effects within the tested concentration rage (0.17–1.2 mg/kg).Even though CBZ was less toxic compared to EP-CBZ, CBZ is found in the environment at much higher concentrations and therefore causes a higher potential risk for sediment dwelling organisms compared to its metabolites. Nevertheless, the current study illustrates the importance of including commonly found metabolites into the risk assessment of parent substances.

Hormesis depends upon the life-stage and duration of exposure: Examples for a pesticide and a nanomaterial

Tests to assess toxic effects on the reproduction of adult C. elegans after 72h exposure for two chemicals, (3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)), also known as diuron, and silver nanoparticles (Ag NPs) indicated potential, although not significant hormesis. Follow up toxicity tests comparing the potential hormesis concentrations with controls at high replication confirmed that the stimulatory effect was repeatable and also statistically significant within the test. To understand the relevance of the hormesis effects for overall population fitness, full life-cycle toxicity tests were conducted for each chemical. When nematodes were exposed to DCMU over the full life-span, the hormesis effect for reproduction seen in short-term tests was no longer evident. Further at the putative hormesis concentrations, a negative effect of DCMU on time to maturation was also seen. For the Ag NPs, the EC50 for effects on reproduction in the life-cycle exposure was substantially lower than in the short-term test, the EC50s estimated by a three parameter log logistic model being 2.9mg/L and 0.75mg/L, respectively. This suggests that the level of toxicity for Ag NPs for C. elegans reproduction is dependant on the life stage exposed and possibly the duration of the exposure. Further, in the longer duration exposures, hormesis effects on reproduction seen in the short-term exposures were no longer apparent. Instead, all concentrations reduced both overall brood size and life-span. These results for both chemicals suggest that the hormesis observed for a single endpoint in short-term exposure may be the result of a temporary reallocation of resources between traits that are not sustained over the full life-time. Such reallocation is consistent with energy budget theories for organisms subject to toxic stress.

Effect of bis(tributyltin) oxide on reproduction and population growth rate of calanoid copepod Schmackeria poplesia

A full life-cycle toxicity test, combined with histology, on calanoid copepod Schmackeria poplesia was used to study the effect of bis(tributyltin) oxide (TBTO). The results indicate no sex-specific differences in TBTO toxicity. Long-term mortalities of the copepods exposed to concentrations higher than 20 ng TBTO L−1 were significantly elevated compared with that of control, and larval development was inhibited when they were exposed to 40 and 60 ng TBTO L−1. The percentages of ovigerous females were reduced compared with the control (P<0.01) after 24 days exposure to concentrations higher than 10 ng TBTO L−1. Histological examinations suggest that exposure to TBTO might block the posterior end of the diverticula and inhibits the production of egg sacs. A modified Euler-Lotka equation was used to calculate a population-level endpoint, the intrinsic rate of natural increase (r m), from individual life-table endpoints, i.e. mortality rate, time of release of first brood, sex ratio, the fraction of ovigerous females among all females as well as the number of nauplii per ovigerous female. Apart from the highest TBTO concentration (60 ng L−1), where all females aborted their egg sacs, 20 ng TBTO L−1 was the only concentration that significantly decreased r m compared with that of control (an effect associated with decreased sex ratio). The results show that the S. poplesia is affected by prolonged exposure to low concentrations of TBTO. The full life-cycle toxicity test combined with histology experiments provides more integral understanding of the toxicity of endocrine disrupters.

Extrapolation of available acute and chronic toxicity test data to population‐level effects for ecological risk management of chemicals

An extrapolation approach is proposed using available acute (median lethal or effect concentration) and chronic (no-observed-effect concentration) toxicity test data at the organism level to derive a reference value contributing to the development of predicted-no-effect concentration on population persistence for population-level ecological risk assessment of chemicals. A matrix population model of wild medaka (Oryzias latipes) was employed as the tool to integrate the available organism-level toxicity test data on reproduction and survival into a finite population growth rate (lambda) that provides information regarding the status of the population persistence. After demonstrating the approach using the acute and chronic toxicity test data of alcohol ethyxolate on fish to calculate the reference value defined as the concentration at lambda = 1 (C(lambda=1)), the proposed approach was then evaluated by a comparison of the C(lambda=1) value derived by the extrapolation approach to those C(lambda=1) values calculated by two other approaches, in which different amounts of toxicity information contained in the same full life-cycle toxicity test data set on 4-nonylphenol were employed. It was concluded that this extrapolation approach is widely applicable and is promising for performing population-level ecological risk assessment on a more general basis that can support reasonable chemical management.

Simulation of the population-level effects of 4-nonylphenol on wild Japanese medaka ( Oryzias latipes)

Here we report a structured matrix model for wild Japanese medaka ( Oryzias latipes) and the use of the model to predict the population-level effects of 4-nonylphenol (4-NP) using a stochastic simulation approach. In the model, the natural fecundity and mortality rates of wild medaka were considered inhibited by 4-NP, based on Weibull dose–response models estimated from a full life-cycle toxicity test. The matrix model was simulated according to three scenarios: (1) stochastic daily growth under optimal conditions, (2) stochastic annual growth under conditions of seasonal variation and (3) population dynamics over 3 years undergoing density-regulation. Accordingly, a finite population growth rate, λ, was applied as an endpoint in the first and second scenarios and a quasi-extinction risk in the third scenario. The median and 95% confidence interval (CI) of 4-NP concentrations corresponding to λ = 1 ( C λ=1 ) in the first and second scenarios were 27.5 μg/L (CI: [20.2, 33.0] μg/L) and 17.0 μg/L (CI: [16.0, 17.9] μg/L), respectively. The quasi-extinction risks mounted quickly when the exposure concentration approached C λ=1 . The influence of uncertainties was analyzed, and the C λ=1 was found to be robust against uncertainties in both the mean and the variation of vital rates, whereas the quasi-extinction risk was moderately sensitive to the mean mortality rate. The ignorance of whether the survival of adult madaka should be considered inhibited by 4-NP or not was found to remarkably affect the population-level effects. This study demonstrates an application of C λ=1 in a stochastic sense as a population-level ecological risk assessment (PLERA) endpoint in chemical risk management.

Individual to population level effects of South Louisiana crude oil water accommodated hydrocarbon fraction (WAF) on a marine meiobenthic copepod

Acute toxicities of crude oil and crude oil water accommodated hydrocarbon fraction (WAF) are relatively well documented, but data on the biological effects of chronic exposures to WAF on species and populations are scarce. South Louisiana Sweet crude oil was used to assess the effects of crude oil WAF on the copepod Amphiascus tenuiremis' survival, development and reproduction. Effects were evaluated using a 96-well microplate full life-cycle toxicity test, a test that allows tracking of individuals from the nauplius stage to sexual maturation and reproduction. Briefly, 24-h hatched nauplii were followed to adulthood ( n i = ≥ 120 nauplii/treatment) in individual glass-coated microplate wells containing 200 μL of seawater solution. Treatments consisted of 10%, 30%, 50% and 100% Louisiana WAF, with seawater used as control. Nauplii were monitored through development to adulthood, and sexually mature virgin copepods were mated pairwise in wells containing original rearing treatments. Nauplius-to-copepodite survival was reduced by 57% in exposures to 100% WAF, relative to controls (88 ± 3%), and copepodite-to-adult survival was reduced by 18% in the 50% WAF, relative to controls (98 ± 3%). Analysis of development curves showed that nauplii in the 10% WAF developed significantly faster into copepodites, while nauplii in the 50% WAF developed significantly slower than controls. Although the naupliar developmental rate in the 100% WAF was not significantly different from the control, these nauplii showed an average 1.4 day delay in development into copepodites. Similarly, copepodite development into mature females and males was significantly enhanced by 1.2 to 1.8 days and delayed by 1.9 to 2.2 days ( p < 0.05) in the 10% and 50% WAFs, respectively, compared to controls. Although the copepodite developmental rate in the 100% WAF was not significantly different from the control, these copepodites still showed an average 1.5 and 2.1 day delay in development into females and males, respectively. Analysis of reproductive endpoints showed that fertility was the only endpoint negatively affected by WAFs; reproductive failure increased by 30% and 41% in exposures to 30% and 100% WAF, respectively, compared to controls (3.33 ± 4.71%). Leslie matrix population projections based on empirical microplate data indicated lower production rates through three generations of exposure to WAFs. Furthermore, a comparison between NIST and Louisiana crude oil WAFs using the same life-cycle approach indicated a greater chronic toxicity for the Louisiana WAF and an overall developmental delay in exposures to high WAFs (50% and 100% WAFs) from both crude oil types.

Chronic toxicity of arsenic to the Great Salt Lake brine shrimp, Artemia franciscana

We determined the chronic toxicity of arsenic (sodium arsenate) to the Great Salt Lake brine shrimp, Artemia franciscana. Chronic toxicity was determined by measuring the adverse effects of arsenic on brine shrimp growth, survival, and reproduction under intermittent flow-through conditions. The study commenced with <24-h-old nauplii, continued through reproduction of the parental generation, and ended after 28 days of exposure. The concentrations tested were 4, 8, 15, 31, and 56 mg/L dissolved arsenic. The test was conducted using water from the Great Salt Lake, Utah as the dilution water. Adult survival was the most sensitive biological endpoint, with growth and reproduction somewhat less sensitive than survival. The no observed effect concentration (NOEC) for survival was 8 mg/L, and the lowest observed effect concentration (LOEC) was 15 mg/L dissolved arsenic. The LOEC for growth and reproduction was greater than the highest concentration tested, 56 mg/L. Based on survival, the final chronic value (geometric mean of the NOEC and LOEC) was 11 mg/L dissolved arsenic. The F 1 generation appeared to acclimate to the prior arsenic exposure of the parental generation and was significantly less sensitive than the parental generation. For example, survival for the F 1 generation through day 12 was 100% in 56 mg/L dissolved arsenic, compared to 26% for the parental generation. Growth of the F 1 generation was significantly less than that of the parental generation across all concentrations including the control, indicating a generational difference in brine shrimp growth rather than an arsenic effect. This study represents one of the few full life cycle toxicity tests conducted with brine shrimp.

Tributyltin environmental studies in Chesapeake Bay

This paper presents and discusses all available data on tributyltin (TBT) monitoring and toxicity studies conducted in Chesapeake Bay. TBT evaluations in the water column were more numerous than microlayer, sediment or tissue assessments. Maximum TBT concentrations occurred in marina or harbour areas during the beginning of the boating season; significant reductions were reported during the summer and early fall. Significantly lower TBT concentrations generally occurred in non-marina areas. TBT toxicity data were available for various Chesapeake Bay invertebrates and fish. Few studies have been conducted with phytoplankton. Chesapeake Bay copepods were the most sensitive organism tested. Bivalve embryos were also sensitive to TBT. A comparison of TBT environmental concentrations with toxicity data was attempted. Maximum TBT concentrations reported in the water column of Chesapeake Bay marinas would likely be toxic to some copepods and early life stages of bivalves. Mean TBT values reported in some marinas would also be toxic to sensitive Chesapeake Bay copepods. If laboratory toxicity data are considered a realistic indicator of real world effects, then most of the Chesapeake Bay organisms tested to date would not be affected by TBT concentrations reported in non-marina areas. Full life-cycle toxicity tests are needed to evaluate chronic effects of environmentally realistic concentrations of TBT to Chesapeake Bay biota.